1. Field
This invention pertains to maintenance and operation methods to clean and operate UV water treatment disinfection systems. In particular it pertains to a pre-treatment method before ultraviolet irradiation particularly suited for disinfecting irrigation, wastewaters, and other waters having suspended solids. The pre-treatment method utilizes sulfurous acid to self-agglomerate and precipitate solids from the water fraction for settling or filtration removal and provides acid to reduce mineral scaling and microbial buildup on uv light tubes to improve their performance.
2. State of the Art
Ultraviolet light disinfection is used to disinfect a variety of waters avoiding the need for chlorine. It is particularly suited for disinfecting culinary and wastewaters. According to the United States Office of Water EPA 832-F-99-064 Environmental Protection Agency publication entitled “Wastewater Technology Fact Sheet Ultraviolate Disinfection”, Washington, D.C. September 1999,                “Disinfection is considered to be the primary mechanism for the inactivation/destruction of pathogenic organisms to prevent the spread of waterborne diseases to downstream users and the environment. It is important that wastewater be adequately treated prior to disinfection in order for any disinfectant to be effective . . . .        An Ultraviolet (UV) disinfection system transfers electromagnetic energy from a mercury arc lamp to an organism's genetic material (DNA and RNA). When UV radiation penetrates the cell wall of an organism, it destroys the cell's ability to reproduce. UV radiation, generated by an electrical discharge through mercury vapor, penetrates the genetic material of microorganisms and retards their ability to reproduce. The effectiveness of a UV disinfection system depends on the characteristics of the wastewater, the intensity of UV radiation, the amount of time the microorganisms are exposed to the radiation, and the reactor configuration. For any one treatment plant, disinfection success is directly related to the concentration of colloidal and particulate constituents in the wastewater.        The main components of a UV disinfection system are mercury arc lamps, a reactor, and ballasts. The source of UV radiation is either the low-pressure or medium-pressure mercury arc lamp with low or high intensities.        The optimum wavelength to effectively inactivate microorganisms is in the range of 250 to 270 nm. The intensity of the radiation emitted by the lamp dissipates as the distance from the lamp increases. Low-pressure lamps emit essentially monochromatic light at a wavelength of 253.7 nm. Standard lengths of the low-pressure lamps are 0.75 and 1.5 meters with diameters of 1.5-2.0 cm. The ideal lamp wall temperature is between 95 and 122° F.        Medium-pressure lamps are generally used for large facilities. They have approximately 15 to 20 times the germicidal UV intensity of low-pressure lamps. The medium-pressure lamp disinfects faster and has greater penetration capability because of its higher intensity. However, these lamps operate at higher temperatures with a higher energy consumption.        There are two types of UV disinfection reactor configurations that exist: contact types and noncontact types. In both the contact and the noncontact types, wastewater can flow either perpendicular or parallel to the lamps. In the contact reactor, a series of mercury lamps are enclosed in quartz sleeves to minimize the cooling effects of the wastewater. FIG. 1 shows two UV contact reactors with submerged lamps placed parallel and perpendicular to the direction of the wastewater flow. Flap gates or weirs are used to control the level of the wastewater. In the noncontact reactor, the UV lamps are suspended outside a transparent conduit, which carries the wastewater to be disinfected. This configuration is not as common as the contact reactor. In both types of reactors, a ballast—or control box—provides a starting voltage for the lamps and maintains a continuous current.        